The interpretation timeline
Zechariah 8:19 Douay-Rheims

Thus saith the Lord of hosts: The fast of the fourth month, and the fast of the fifth, and the fast of the seventh, and the fast of the tenth shall be to the house of Juda, joy, and gladness, and great solemnities: only love ye truth and peace.

A.D. 373 – 1871 7 witnesses

Patristic

before A.D. 750
373
A.D.
c. A.D. 296–373
“Therefore, when we come to the feast, we must not treat it as the shadows and pictures that Israel had, for they are fulfilled. Nor should we come to it as we would any ordinary secular feast. Oh, no! Let us go quickly to the Lord, who is himself the feast. We must not look at the feast as a time to delight the appetite and overindulge but as a display of virtue. The feasts of the heathen are made up of laziness and greed. They think idleness is the mark of a feast, and when they feast they do the despicable acts of death and hell. Our feasts, on the other hand, are scenes of virtuous activities and the practice of temperance. The prophetic word says it very clearly, "The fasts of the fourth, fifth, seventh and tenth months shall become feasts of joy and gladness for the house of Judah."”
Source

Scholastic

c. 1100 – 1500
1105
A.D.
Rashi Jewish
1040–1105
“the fast of the fourth [month] The fast of Tammuz, which is the fourth of the months. the fast of the fifth [month] of Av. the fast of the seventh [month] The third of Tishri, when Gedaliah was assassinated. and the fast of the tenth [month] Of Teveth.”

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“And the inhabitants of one city shall go to another,.... Which shows their concern for the spiritual welfare of each other, their zeal for the honour and glory of God, and their readiness to attend divine worship: saying, Let us go speedily to pray before the Lord; for pardoning, justifying, and sanctifying grace which shows their sense of need of these things, and that they are only to be had of the Lord; and that their case required haste, and would admit of no delay: and to seek the Lord of hosts: by prayer and supplication, as before: the Chaldee paraphrase is, "to seek doctrine from the Lord of hosts"; to learn the truths of his Gospel; to know his will, and be informed of the right way of worshipping him, as well as to seek to Christ for life and salvation: I will go also; that is, "this shall say to that", as the Targum supplies it; one shall say to another, and express himself in such language, by way of example and encouragement.”
Source
1832
A.D.
Adam Clarke Methodist
1762–1832
“The fast of the fourth month - To commemorate the taking of Jerusalem; Kg2 25:3; Jer 39:2; Jer 52:6, Jer 52:7. The fast of the fifth - In memory of the ruin of the temple, Kg2 25:8; Jer 52:12, Jer 52:13. The fast of the seventh - For the murder of Gedaliah, Jeremiah 41:1-17. The fast of the tenth - In commemoration of the siege of Jerusalem, which began on the tenth day of the tenth month; Kg2 25:1; Jer 52:4; Eze 24:1, Eze 24:2; and see on Zac 7:3 (note), Zac 7:5 (note). Cheerful feasts - Ye shall find all your evils so completely redressed, that these mournful fasts shall be turned into joyful feasts.”
Source
1849
A.D.
1774–1849
“Fast. They fasted on the ninth day of the fourth month, because on that day Nabuchodonosor took Jerusalem, Jeremias lii. 6. On the tenth day of the fifth month, because on that day the temple was burnt, Jeremias lii. 12. On the third day of the seventh month, for the murder of Godolias, Jeremias xli. 2. And on the tenth day of the tenth month, because on that day the Chaldeans began to besiege Jerusalem, 4 Kings xxv. 1. All these fasts, if they will be obedient for the future, shall be changed (as is here promised) into joyful solemnities. (Challoner) — They had only inquired about the fasts of the fifth and seventh months but the two others were also to be omitted in times of joy. (Worthington) — The Jews still observe all four. (Basnage v. 16.) — They fast on the seventeenth of the fourth month, because the breach was then made in the walls, (Calmet) and Moses broke the tables of the law, according to the Jews, in St. Jerome. The ninth of the fifth month is also kept instead of the tenth, on which day the city was taken by the Chaldeans; (Calmet) and the Romans burnt the temple in the same month, as the Israelites had then formerly been sentenced to wander in the desert. (St. Jerome) — It would be difficult for the Jews to prove all these assertions.”
Source
1863
A.D.
1796–1863
“On the ninth day of the fourth month N abuohodonoeor took Jerusalem. Jer. 52 : 6. Rt. Jerome, on the authority of the Jews, says that they fasted on the seventeenth day of the same month, in commemora- tion of the breaking of the tables of the law. M This fast is said to have been on account of the murmuring on the return of the explorers, and the sentence decreed against the murmurers, that they should wander and perish in the desert The temple was burnt on the tenth day of the fifth month. Jer. 52 : 12.”
Source
1871
A.D.
1871
“fast of . . . fourth month--On the fourth month of the eleventh year of Zedekiah's reign, on the ninth day, Jerusalem was taken (Jer 39:2; Jer 52:6-7). It was therefore made a fast day. fifth . . . seventh--(See on Zac 7:3; Zac 7:5). tenth--On the tenth month and tenth day, in the ninth year of Zedekiah, the siege began (Jer 52:4). therefore love the truth--or, "only love." English Version is better. God's blessing covenanted to Israel is not made to depend on Israel's goodness: but Israel's goodness should follow as the consequence of God's gracious promises (Zac 8:16-17; Zac 7:9-10). God will bless, but not those who harden themselves in sin.”
Source
Modern · 1953 →

The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.